Introduction

Proton therapy is a radiation treatment that precisely delivers a beam of protons (high-energy particles) to damage and eliminate tumour cells. The specific properties of protons allow for accurate tumour targeting, minimising damage to the adjacent healthy tissue.

Overview

Proton therapy, or proton beam therapy, is a form of radiation treatment that employs high-powered energy to treat cancer. This type of therapy uses positively charged protons to deliver precise, high-powered energy that damages the DNA within cancer cells. By focusing on the mutations of cancer cells, it eradicates them and stops them from replicating. With proton therapy, energy delivery can be more precisely controlled, resulting in fewer side effects compared to X-ray radiation. This approach directly targets the treatment area, reducing harm to nearby tissues. For this reason, proton therapy is considered a good option for treating critical areas like the brain. 

However, only a few studies have compared the two therapies, leaving it inconclusive whether proton therapy is more effective in extending life. Proton therapy is done by radiation oncologists, who are medical professionals with specialised expertise in using radiation to treat cancer. Although this type of treatment is not yet widely available, new centres are being established across the United States and globally. The article discusses what proton therapy is, how it works, and its advantages, disadvantages, and risks.

Proton therapy vs. Traditional Radiation

Radiation therapy or radiotherapy, often using X-rays, is the main cancer treatment for nearly 50% of patients. However, it can cause significant side effects and affect quality of life because delivering a lethal dose to cancer cells often requires irradiating surrounding healthy tissue.

Traditional radiotherapy uses an external radiation beam that weakens as it travels through the body. For deep tumours, this means healthy tissue in front of the tumour receives a high dose of radiation, and tissue behind the tumour may also get irradiated, which can be an issue for delicate areas such as the brain and spinal cord.

Recent advancements in radiotherapy, like image-guided and intensity-modulated techniques, combined with targeted drugs and immunotherapy, have improved treatment. Proton beam therapy offers even greater precision, delivering lower doses to healthy tissues and reducing side effects. Despite this, many tumours remain resistant to radiation, emphasising the need for further research to improve treatments and reduce harm to healthy tissues.¹

Which cancers are commonly treated with proton therapy?

Proton therapy is used to treat various tumours such as: 

• Brain tumours
• Breast cancer
• Cancer in children
• Pituitary gland tumours
•  Eye melanoma
• Oesophageal cancer
• Head and neck cancers
• Spinal tumours
• Prostate cancer
• Liver cancer
• Lung cancer
• Pancreatic cancer
• Sarcoma
• Lymphoma
• Tumours in the base of the skull

Who can receive this kind of treatment?

In general, radiation oncologists use proton therapy for tumours located near critical areas of your body, such as areas of your brain or spinal cord. This treatment is for tumours that haven’t metastasised. It may also be to treat children with cancer.

How does Proton Therapy work?

Proton Beam Therapy affects both normal and cancer cells. Cancer cells are more sensitive to radiation than normal cells, making them more likely to be destroyed. However, normal cells can heal, so the damage is usually short-term. Additionally, protons cause less normal tissue to be irradiated, leading to fewer and less severe side effects during and after treatment.

For therapeutic applications, protons are accelerated using a particle accelerator such as a synchrotron or cyclotron, each with its own benefits and drawbacks. A special device, usually a 360-degree rotating gantry, uses a strong magnet to focus the proton stream into a narrow 5-millimeter-wide beam. The magnet controls the direction of the beam to target the tumour from various angles as the gantry rotates around the patient. The proton beam's energy can be changed based on the tumour's depth, so different tumour parts receive varying amounts of radiation.

Cyclotrons produce a steady stream of protons, are more compact, and deliver higher beam intensity, with protons reaching the machine's maximum energy (e.g., 230 MeV). On the other hand, synchrotrons accelerate protons in pulses to the required energy level. Synchrotrons offer greater energy flexibility, a narrower energy spread, and lower power consumption.² 

Positively charged protons can damage DNA by directly colliding with its negatively charged molecules, leading to structural disruptions to the DNA. They also cause indirect damage by generating reactive oxygen species (ROS). Their higher energy levels make protons more efficient than photons at damaging cancer cells while limiting harm to healthy tissues.³  

What are the benefits of Proton Therapy?

The main advantage of proton therapy is the potential to target tumour cells more precisely. A higher concentration of radiation targets the tumour, while the surrounding healthy tissue receives significantly less exposure. This results in reduced side effects and a lower risk of complications.

Proton therapy offers several advantages:

• Functions such as memory can be preserved when the tumour is adjacent to these areas
• Minimising risks for children with cancer, who frequently experience long-lasting side effects from intensive treatments
• Reducing radiation exposure to crucial organs like the lungs, or during the treatment of breast or spine cancers
• Preventing extra radiation to previously treated areas, if a tumour reappears near or at its original site

What are the disadvantages of Proton Therapy?

Disadvantages of proton therapy include:

• Availability: Only a few centres worldwide offer proton beam therapy
• Increased planning time: Radiation therapy specialists require a few weeks to plan proton therapy
• High cost:  Proton therapy is more expensive than photon radiation therapy because it requires sophisticated, specialised equipment, which is costly to manufacture and operate

What are the risks of proton therapy?

Although the highest dose of radiation is targeted to the tumour, proton therapy can still irradiate healthy tissue. By affecting less healthy tissue, the side effects may be milder, and the risk of secondary cancers from radiation is reduced.

Common side effects include:

• Fatigue
• Hair loss in the area being treated
• Soreness in the treated area
• Skin redness in the treated area

Late side effects include:

• Infertility
• Lymphedema
• Brain and spinal cord changes

Pre-Treatment Planning and Duration for Proton Therapy

Before treatment, one or two CT scans and possibly an MRI scan are required to plan the proton therapy. The duration of the treatment typically ranges from three to seven weeks, depending on the type of cancer.

Summary

Proton therapy is an advanced radiation treatment that uses high-energy protons to target and destroy tumour cells with precision. Unlike conventional X-ray radiation, proton therapy's unique properties allow for accurate targeting of tumours while minimising damage to surrounding healthy tissues. This technique is particularly beneficial for treating tumours located near critical areas such as the brain and spinal cord. 

Proton therapy offers several advantages, including reduced side effects and lower risk of secondary cancers due to its ability to deliver higher doses of radiation directly to the tumour. The treatment involves complex equipment, including synchrotrons or cyclotrons, to accelerate protons and a rotating gantry to direct the beam accurately. Despite its benefits, proton therapy is not widely accessible, is expensive, and requires extensive planning time. The therapy's effectiveness compared to traditional radiation therapy is still under study, particularly regarding long-term outcomes. Proton therapy can be applied to treat different types of cancers, such as those in the brain, breast, and spine, and is especially effective for children and tumours close to delicate areas. 

However, the treatment may still affect healthy tissues, leading to common side effects such as fatigue and hair loss, and potentially late effects like infertility and lymphedema. The planning involves CT and possibly MRI scans, with treatment duration ranging from three to seven weeks.